Fossils Preserved in Maine Sediments

Introduction

Continental glaciers covered Maine during the last Ice Age (refer to Maine's glacial geology history). The weight of these glaciers depressed the land surface below sea level, and as the glaciers melted and retreated, sea water flooded the Maine coast. Fine silt and clay washing out of the glaciers covered the seafloor, creating a layer of glaciomarine mud now called the Presumpscot Formation (PDF, 1.8Mb). A variety of marine organisms lived in these coastal waters, and when they died, continued deposition of clay on the coastal seafloor buried their shells. Later, the land surface rebounded and the ocean receded, leaving large areas of clay above sea level in coastal Maine.

Shells buried in these marine clays can be extremely well preserved, retaining their color and luster. Even though they may be over 12,000 years old, they look like modern shells. Fossils of a variety of marine organisms have been found in the Presumpscot Formation. Most common are invertebrate shells such as clams, scallops, mussels, snails, and barnacles. However, fish and mammal remains have been found as well, including a walrus and even a mammoth that was washed into the ocean after it had died (these bones are on display in the Maine State Museum). Fossil spruce wood, needles, cones have also been found buried in this clay.